Conventional design practice is to route individual process control and safety signals from the process interface building (PIB) and/or the central control room (CCR) to field devices, including sensors and final elements. Sensors can include pressure switches and transmitters, level switches and transmitters, temperature switches and transmitters, position and limit switches, vibration monitors, among other instruments. Final elements can include electric solenoids, actuators and positioners for controlling the starting and stopping of motors, the speed of such motors, the opening and closing of valves either fully or to a particular position, and so forth. Where field devices require separate power, this is also conventionally provided from the PIB or CCR. These prior art designs require numerous control system input/output (I/O) racks at the PIB or CCR and large quantities of cables and conduit to and from the field. The introduction of Fieldbus Foundation (FF) H1 technology offered the ability to “multi-drop” instruments at the field level. However, the net cost savings achieved by major petrochemical projects due to reduction in field wiring with FF H1 systems has been limited due to the 31.25 Kbit/sec communications speed, which limits the number of field devices that could effectively share a common FF H1 segment. In addition, FF H1 systems and other conventional control systems require large system rack cabinets within the CCR or PIB to provide the field-to-control system interface. Existing conventional “remote I/O” technology falls short of providing a completely stand-alone termination, power supply, state-based logic, and signal conversion capability.
What is required is a system that enables the conversion of instrumentation and control signals to be converted to high speed digital communications “in the field” instead of within the vendor I/O racks in the CCR or PIB. Such a system would greatly reduce the number of interconnecting hardwired cables, conduits, cable trays and other raceways that currently must to be routed between the field mounted junction boxes and the PIB or CCR, as well as reducing the number of rack cabinets required within the CCR or PIB. This significant reduction in plant hardware and infrastructure requirements would provide substantial costs savings.
Such a system would provide the end user with greater flexibility to communicate with a diverse set of field devices over a common high speed digital communications network.
Also comprehended is a field-mounted control interface, in which a field versatile control gateway (FVCG) mounted within a smart junction box (SJB) allows connectivity within a single enclosure of a diverse set of oil field control devices, such as sensors and valves deployed at oil/gas wellsites. The FVCG/SJB provides a complete control function in the field of monitoring critical inputs, checking parameters against allowable limits and executing required actions to provide for safe and reliable oil/gas wellsite operations. The FVCG/SJB includes provisions for conversion of the multitude of field communications protocols used in the industry, the ability to recognize device level “health” diagnostic indicators and apply local state-based logic to enhance reliability and safety of the overall safety instrumented function (SIF) based on user-defined criteria, taking into account criteria such as required risk reduction, appropriate response to faults, and the installed device redundancy. Communications back to the central control room is made via the high speed communications enabled by the FVCG/SJB.
For convenience, the following is a listing of abbreviations of terms that are used in discussing the prior art and describing the invention:
CCR: central control room
CPU: central processing unit
DCS: distributed control system
EI: Ethernet Interface
ESD: emergency shutdown
FF: Fieldbus Foundation
FVCG: field versatile control gateway
I/O: input/output
ISA100: a wireless protocol of the International Society of Automation (ISA)
HSL: High Speed Link using single-mode fiber, multimode fiber, and Ethernet
ISCI: Intelligent safety and control integrator
JB: junction box
PIB: process interface building
PRC: plant routing controller
SIF: safety instrumented function
SJB: smart junction box